A red rag to a bull?

[Guest]

Test No. incompl/inter-2 "Like a red rag", question 1

Don't talk to him about politics because it's like a ......... rag to a bull.

(a) blue
(b) white
(c) red
(d) black

Test No. incompl/inter-2 "Like a red rag", answer 1

Don't talk to him about politics because it's like a red rag to a bull.

Correct answer: (c) red

Your answer was: incorrect
Don't talk to him about politics because it's like a blue rag to a bull.
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why?

[Torsten]

Because the colour red is thought to infuriate bulls. Have you ever seen a Torero - a Spanish bullfighter? Do you remember what he was holding in this hands? Yes, it was a red rag!
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Test Of English for International Communication
TOEIC Preparation & TOEIC Vocabulary

[BrownieGirl]

The phrase Red rag to a bull, comes from the bullfights, which use either a red rag, or a cloth lined with red. The colour is insignificant to the bull.
They attack because they feel threatened, not because of the colour of the cloth, bulls see, according to scientists in monochrome.